1. Field of the Invention
The invention is directed to a flow limiting throttle element for restricting the flow of a fluid guided in a delivery line.
2. Description of the Prior Art
Throttle points are installed for the purpose of a simple regulation of the rate of a fluid flowing through a delivery line. Such throttles are fundamentally distinguished as nonadjustable and adjustable. Nonadjustable signifies that the desired reduction in rate is determined once and for all by the type of constriction and its cross section so that the rate of flow depends only on viscosity, i.e. is primarily a function of temperature. In an adjustable throttle, the cross section of the reduction can be changed in stages or in a continuous manner from the outside. This can be actuated mechanically, hydraulically, pneumatically or electrically. If throttling is to be effected in only one flow direction and a free flow is required when the flow direction is reversed, a so-called throttle check element or flow limiting throttle element is selected for controlling the rate of flow.
In order to achieve the desired throttling, at least one or more small bore holes are arranged in the actual throttle body in a simple manner so that the fluid which is supplied over a substantially larger cross section is pressed through this constriction. This construction has the disadvantage that particles of dirt can easily lodge in the narrow bore holes and under certain circumstances can completely block flow. This is unacceptable for critical applications such as in aircraft construction for actuating important functional elements. For this reason, it is recommended that a sieve be arranged in these locations for such applications in order to catch particles of dirt. Since the structural component parts are generally very small, the arrangement of a sieve is often difficult in terms of construction, especially since the sieve must be arranged so as to be exchangeable in many cases to prevent clogging.
U.S. Pat. No. 3,595,265 discloses a self-cleaning test valve which provides for a free flow of fluid in the "open" position and a reduced flow of fluid in the "closed" position. A continuous slot communicating with two overflow ducts arranged in the outer surface area of the valve body is arranged on one end of the valve body to throttle the flow. The sealing fit is formed by the end face of the valve body with the inner end face of the bore hole of the housing in which the valve body is arranged so as to be displaceable axially. The necessary contact pressure force is produced by a spring which is arranged in the bore hole of the housing and is supported on the valve body on one side and at a plug arranged in the bore hole on the other side. The housing of the valve is provided with two working connections. One working connection is arranged coaxially with the bore hole of the housing and the other working connection opens into the bore hole at right angles thereto. In the event that the narrow throttle slot becomes clogged with particles, the slot may be rinsed out in the "open" position of the valve. However, in order to do this the pressure in the working connection coaxial to the bore hole must be high enough to overcome the opposing spring force. In so doing, the prevailing counter-pressure in the other working connection must also be taken into account. One disadvantage of this valve is that it cannot be easily installed in a fluid line because the working connections are arranged at right angles to one another and the slot can only be rinsed out in the "open" position. A further disadvantage consists in the costly manufacture of the valve housing with the long, accurately aligned tailored bore hole and the sealing inner end face. The cost of construction is further increased by the arrangement of a plug which is tight against high pressure for supporting the spring.
A flow limiting throttle element of the generic type is known from DE-GM 7016093. This flow limiting throttle element has a pressure-tight housing with two working connections arranged coaxially to one another. A valve body in the form of a truncated cone which is freely displaceable axially is arranged in a bore hole of the housing and is provided at one end with a slot forming an overflow duct. The sealing fit is formed by the conical surface of the valve body in cooperation with a corresponding surface in the housing. A bore hole with a diameter between 0.07 and 0.1 mm is arranged on the small end face of the valve body for throttling the flow of gas.
The continuous slot is closed by the conical surface of the housing in the "closed" position and the gas can only flow through the small bore hole of the valve body. In the "open" position, the continuous slot and the annular space formed between the conical outer surface area of the valve body and the bore hole of the housing forms overflow ducts which provide for a free passage of the gas.
A disadvantage of this construction is that the valve body is guided at only one end, which does not exclude tilting. Also, the large sealing surfaces which are adapted to one another are costly to produce and it is not possible to rinse out the bore hole if the latter should become clogged.